Question about cleaning up freeplay / backlash in Enco 12x36 lathe leadscrew

[OnyxSkyDV]

So, I have noticed that my leadscrew has some backlash / freeplay in it. With an indicator on the ways, up against the carriage, with halfnuts engaged, moving the carriage handwheel will read about 20thou of free play in the leadscrew.

I have to assume this is not helping my threads at all, and am looking at how to fix this. The drive socket that comes out of the headstock, which the leadscrew attaches to via a roll pin, will visibly move in and out, so I am sure that at least some of this free play is there, and not necesarily worn halfnuts.

A friend of mine has suggested making a thrust bearing for the tailstock end of the leadscrew to remove that freeplay, but I am curious if anyone else has had this issue and how they resolved it.

Thanks!


Onyx

 

[Sparweb]

Hi
Bumping up this old thread because I have the same problem.

My first investigation into the problem started at the headstock. In the leascrew of my lathe it's mounted into the socket with a taper pin and it looks very secure there. The problem is at the tailstock end, then, probably the thrust bearing. But there's not an obvious way to get into it without (it seems) opening up all 3 of the thrust bearings at the same time. That's a whole lot of pieces falling apart simultaneously, unless I've misjudged.

The freeplay is more than 1/16" so I really can't thread anything at all.

My lathe is a 1986 "Central Machinery" 12x36 lathe, not too different from the Enco and Grizzly lathes more commonly seen now.
Would a current Grizzly maintenance manual be of any help?

Thanks in advance!

 

[CoDef911]

So, it's odd that this is the open thread today. I have just found the exact same thing in mine, while learning how to thread. What I have is the backlash both at the leadscrew mount, and coming from the gears.
What I've read, is that it is what it is. And you CAN thread with it, it just takes knowing that it's there, and how to deal with it.
I'm learning how to properly cut threads now. And managed to cut a pretty good 1/2×28 on an old Weatherby rifle today.
This Old Tony on YT has a very good video on basic threading. In his video, he showed his machine with the same backlash issue, and dealt with it by having the feed take up the backlash on its way onto the piece. I watched his video, and put hands on my machine as he was doing his.
I'm not aware of the proper fix, but it showed me you can still do it, just make sure you figure it into the setup.

 

[Sparweb]

OK
I figured out a better way that allows me to cut a thread, but the results were only just barely functional, not ideal.
I dug a very old book on machining practices from the 1920's so that I could avoid the space modern books waste on CNC.
You may be surprised but my 1986 lathe works just like the lathe described in that book printed in 1919.
For those who want to see: Turning and Boring, by Franklin D. Jones
You can read it or download it from Gutenberg.org

With a much more detailed description of what's going on when I engage the thread indicator, I realized that I can set up my lathe to NEVER disengage it through the whole threading operation. That was the problem - unlocking and re-locking the half-nut on successive passes, but picking up the leadscrew at a different position because of the free play.

And... yes, there's a This Old Tony video on thread cutting where he does this, and I watched it... in my defense that was in 2016 and I didn't get my lathe until last year so there's been all this time to forget the details. But a nice excuse to re-watch a classic episode of TOT so it's been a nice morning overall.

 

[RJSakowski]

Most lathes have backlash/lost motion in the lead screw. Even if you could eliminate the lead screw lost motion entirely, you still have lost motion in the gear train by virtue of the fact that the gears require some clearance when meshing to function properly.

This is not a problem as threading is always done in one direction only. When reaching the end of a pass, the cutter is retracted and the carriage move back to slightly beyond the starting point to allow the free play to be taken up before starting the cut.